1) Field of the Invention
The invention relates to polyvinyl alcohol-stabilized copolymers of 1,3-dienes with methacrylates and/or acrylates in the form of their aqueous polymer dispersions or polymer powders redispersible in water, and to a process for their preparation and their use.
2) Background Art
As explained in WO-A 97/15603, polymer dispersions which are stabilized with polyvinyl alcohol (PVA1) have characteristic rheology and tack properties, so that, in contrast to emulsifier-stabilizer dispersions, they are particularly suitable for coating and adhesive applications. For example, paper packaging adhesives prepared using emulsifier-stabilized copolymer dispersions have poor machine running properties compared with PVA1-stabilized copolymer dispersions, owing to the fine particles (particle size in general  less than 400 nm), the rheology and the low surface tension of the emulsifier-stabilized dispersion. A disadvantage of the adhesives prepared using vinyl ester-based or acrylate-based copolymer dispersions is that, owing to their generally relatively high glass transition temperature (Tg) or the minimum film formation temperature (MFT), the addition of plasticizer for processing is necessary.
Using vinyl acetate/ethylene copolymer dispersions, it is possible to prepare plasticizer-free paper packaging adhesives which have improving adhesion properties with increasing ethylene content and hence associated declining Tg. A disadvantage of the adhesives prepared using polyvinyl alcohol-stabilized vinyl acetate/ethylene copolymer dispersions is that the reduction in Tg due to copolymerization with ethylene is subject to limits owing to the crystallization of the vinyl acetate/ethylene copolymers.
By copolymerizing 2-ethylhexyl acrylate, glass transition temperatures Tg down to below xe2x88x9250xc2x0 C. can be achieved with polymer dispersions based on acrylate polymers. However, pure acrylate dispersions on an alkaline substrate release the corresponding alcohol at pH greater than 9, owing to hydrolysis of the ester group. Thus, 2-ethylhexyl alcohol is released from 2-ethylhexyl acrylate and may be released into the surrounding air. Moreover, by oxidation of 2-ethylhexyl alcohol to the corresponding acid, secondary products which are not toxicologically safe can be produced. A further side effect is that polyacrylic acid domains having a very high Tg are obtained by hydrolysis of the ester group. The high Tg in turn has an adverse effect on the viscoelastic modulus of the resin and hence a negative effect on a number of performance characteristics such as wetting and adhesion.
It was therefore the object to provide a hydrolysis-stable dispersion or powder type whose polymer resin can be prepared in a wide Tg range (xe2x88x9280xc2x0 C. less than Tg less than +100xc2x0 C.). The aqueous dispersion or redispersion should have the advantageous Theological properties (machine running properties) of polyvinyl alcohol-stabilized vinyl ha ester or acrylate dispersions and should have good adhesion to a very wide range of substrates such as paper, plastics and minerals, even in the case of low Tg and in the absence of plasticizer.
This object was achieved by a process by means of which polyvinyl alcohol-stabilized copolymers of 1,3-dienes with methacrylates and/or acrylates are obtainable in the form of their aqueous polymer dispersions or polymer powders redispersible in water.
DE-A 2442121 (GB-A 1438449) disclosed that polyvinyl alcohol is not effective as a sole dispersant in the preparation of polymers of (meth)acrylates or butadienes and has therefore always been used as a mixture with emulsifiers. DE-A 2442121 therefore recommends the use of a polyvinyl alcohol modified with alkali metal olefin sulfonate for the preparation of polyvinyl alcohol-stabilized polymers of (meth)acrylate or butadiene monomers. The disadvantage is that this too is an ionic stabilizer and the disadvantages occurring in the case of emulsifiers and described above therefore also occur.
WO-A 97/15603 describes butadiene/(meth)acrylate copolymers which are stabilized with polyvinyl alcohol and emulsifiers and are obtained by grafting the polyvinyl alcohol moiety onto the copolymer by means of a functionalized silane, especially mercaptotrialkoxysilane.
U.S. Pat. No. 5,200,459 recommends copolymerization in the presence of a stabilizing solvent, in particular from the group consisting of the alcohols, for the preparation of polyvinyl alcohol-stabilized, aqueous butadiene copolymer latices.
WO-A 99/28360 discloses the preparation of polyvinyl alcohol-stabilized styrene/butadiene copolymer dispersions or dispersion powders. However, styrene-containing copolymer dispersions have the disadvantage of having viscoelastic polymer properties disadvantageous for many applications (for example in adhesives) (poor deformability). In the copolymer styrene produces polymer domains having a high Tg; these lead to relatively disadvantageous viscoelastic resin properties. This results, for example in the case of adhesives, in poorer wetting properties and poorer tack.
DE-A 19548313 (U.S. Pat. No. 5,733,944) and EP-A 744418 (U.S. Pat. No. 5,733,944) disclose processes for the preparation of aqueous dispersions of butadiene/(meth)acrylate copolymers which are prepared in the presence of a protective colloid and an emulsifier.
The invention relates to emulsifier- and solvent-free copolymers, stabilized with nonionic polyvinyl alcohol as protective colloid, of 1,3-dienes with methacrylates and/or acrylates in the form of their aqueous polymer dispersions or polymer powders redispersible in water, obtainable by emulsion polymerization and optionally drying of the polymer dispersions obtained thereby, from 10 to 100% by weight of the amount of polyvinyl alcohol being initially introduced before the initiation of the polymerization and the remaining amount being metered in during polymerization, and the addition of polyvinyl alcohol and the comonomers being controlled in such a way that, during the polymerization, the amount of protective colloid is always from 1 to 70% by weight of the total amount of free comonomers.
The invention furthermore relates to a process for the preparation of emulsifier- and solvent-free copolymers, stabilized with polyvinyl alcohol as a protective colloid, of 1,3-dienes with methacrylates and/or acrylates in the form of their aqueous polymer dispersions or polymer powders redispersible in water, by emulsion polymerization of a mixture containing one or more comonomers from the group consisting of the 1,3-dienes and one or more comonomers from the group consisting of the methacrylates and acrylates, in the presence of from 1 to 15% by weight, based on the total weight of the monomers, of one or more polyvinyl alcohols and optionally drying of the polymer dispersions obtained thereby, from 10 to 100% by weight of the amount of polyvinyl alcohol being initially introduced before the initiation of the polymerization and the remaining amount being metered in during polymerization, and the addition of polyvinyl alcohol and of the comonomers being controlled in such a way that, during the polymerization, the amount of protective colloid is always from 1 to 70% by weight of the total amount of free comonomers.
Suitable 1,3-dienes are 1,3-butadiene and isoprene, 1,3-butadiene being preferred. Suitable methacrylates and acrylates are those of straight-chain and branched alcohols having 1 to 10 carbon atoms. Preferred methacrylates are methyl methacrylate, ethyl methacrylate, propyl methacrylate and n-butyl methacrylate. Methyl methacrylate is particularly preferred. Preferred acrylates are methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate t-butylmeth acrylate and 2-ethylhexyl acrylate. Methyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred.
If required, from 1 to 30% by weight, based on the total weight of the monomer mixture, of further monomers copolymerizable with 1,3-dienes and with the (meth)acrylates such as ethylene, vinyl chloride or vinyl esters of straight-chain or branched carboxylic acids having 1 to 15 carbon atoms, for example vinyl acetate, and vinyl esters of alpha-branched monocarboxylic acids having 5 to 11 carbon atoms such as VeoVa9(copyright) or VeoVa10(copyright) (trade names of Shell), can also be copolymerized.
If required, from 0.05 to 10% by weight, based on the total weight of the monomer mixture, of auxiliary monomers may also be copolymerized. Examples of auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid and maleic acid; ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide and acrylonitrile; mono- and diesters of fumaric acid and maleic acid such as the diethyl and diisopropyl esters, and maleic anhydride, ethylenically unsaturated sulfonic acid and its salts, preferably vinylsulfonic acid or 2-acrylamido-2-methylpropanesulfonic acid. Further examples are precrosslinking comonomers such as polyethylenically unsaturated comonomers, for example divinyl adipate, diallyl maleate, allyl methacrylate or triallyl cyanurate, or postcrosslinking comonomers, for example acrylamidoglycolic acid (AGA), methylacrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylol allylcarbamate, alkyl ethers such as isobutoxy ether, or esters of N-methylolacrylamide, of N-methylolmethacrylamide and of N-methylol allyl carbamate. Comonomers having epoxide functional groups such as glycidyl methacrylate and glycidyl acrylate, are also suitable. Further examples are comonomers having silicon functional groups such as acryloyloxypropyltri(alkoxy)silanes and methacryloyl-oxypropyltri(alkoxy)silanes, vinyl trialkoxysilanes and vinylmethyldialkoxysilanes, it being possible, for example, for ethoxy and ethoxypropylene glycol ether radicals to be present as alkoxy groups. Monomers having hydroxyl or CO groups may also be mentioned, for example hydroxyalkyl methacrylates and acrylates such as hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate, and compounds such as diacetoneacrylamide and acetylacetoxy methyl acrylate or methacrylate.
The choice of monomers or the choice of the amounts by weight of the comonomers is made in such a way that in general a glass transition temperature Tg of from xe2x88x9280xc2x0 C. to +100xc2x0 C., preferably from xe2x88x9250xc2x0 C. to +50xc2x0 C., particularly preferably from xe2x88x9220xc2x0 C. to +40xc2x0 C., results. The glass transition temperature Tg of the polymers can be determined in a known manner by means of differential scanning calorimetry (DSC). The Tg can also be calculated approximately beforehand by means of the Fox equation. According to Fox T. G., Bull. Am. Physics Soc. 1, 3, page 123 (1956), the following is applicable: 1/Tg=x1/Tg1+x2/Tg2+ . . . +xn/Tgn, where xn represents the mass fraction (% by weight/100) of the monomer n and Tgn is the glass transition temperature in degrees Kelvin of the homopolymer of the monomer n. Tg values for homopolymers are listed in Polymer Handbook, 2nd Edition, J. Wiley and Sons, New York (1975).
Mixtures comprising from 20 to 80% by weight, preferably from 30 to 55% by weight, of (meth)acrylates, in particular methyl methacrylate, and from 20 to 80% by weight, preferably from 45 to 70% by weight, of 1,3-diene, in particular 1,3-butadiene, are particularly preferred, it being possible for mixtures optionally also to contain one or more of the above-mentioned auxiliary monomers in the stated amounts, and the amounts in % by weight sum to 100% by weight.
The preparation of the polyvinyl alcohol-stabilized copolymers is carried out by the emulsion polymerization process in the absence of emulsifier, the polymerization temperature being in general from 40xc2x0 C. to 100xc2x0 C., preferably from 60xc2x0 C. to 90xc2x0 C. The polymerization with 1,3-butadiene is effected under the vapor pressure of the reaction mixture, in general between 2 and 15 bar, at the chosen polymerization temperature. In the copolymerization of gaseous comonomers, such as ethylene or vinyl chloride, it is also possible to employ a higher pressure, in general between 5 bar and 100 bar.
The polymerization is initiated with the at least partially water-soluble, thermal initiators or redox initiator combinations customarily used for the emulsion polymerization. Suitable organic initiators are hydroperoxides such as tert-butyl hydroperoxide, tert-butyl peroxopivalate, cumyl hydroperoxide or isopropylbenzene monohydroperoxide, or azo compounds such as azobisisobutyronitrile. Suitable inorganic initiators are the sodium, potassium and ammonium salts of peroxodisulfuric acid. Said initiators are used in general in an amount of from 0.05 to 3% by weight, based on the total weight of the monomers.
Combinations of said initiators with reducing agents are used as redox initiators. Suitable reducing agents are the sulfites and bisulfites of the alkali metals and of ammonium, for example sodium sulfite, the derivatives of sulfoxylic acid, such as zinc or alkali metal formaldehyde sulfoxylates, for example, sodium hydroxymethanesulfinate, and ascorbic acid. The amount of reducing agent is preferably from 0.01 to 5.0% by weight, based on the total weight of the monomers.
Suitable polyvinyl alcohols are nonionic, partially hydrolyzed polyvinyl acetates and nonionic, partially hydrolyzed polyvinyl esters which have been rendered hydrophobic, and mixtures thereof, it also being possible to use said polyvinyl alcohols as a mixture with further protective colloids.
Nonionic, partially hydrolyzed polyvinyl acetates having a degree of hydrolysis of from 80 to 95 mol % and a Hxc3x6ppler viscosity (4% strength aqueous solution, DIN 53015, Hxc3x6ppler method at 20xc2x0 C.) of from 1 to 30 mPas, preferably from 2 to 15 mPas are particularly preferred.
Nonionic, partially hydrolyzed polyvinyl esters which have been rendered hydrophobic and, in the form of a 2% strength aqueous solution, produce a surface tension of  less than 40 mN/m are also preferred. Suitable partially hydrolyzed polyvinyl esters which have been rendered hydrophobic can be obtained, for example, by rendering polyvinyl acetate hydrophobic by copolymerization of vinyl acetate with hydrophobic comonomers. Examples of these are isopropenyl acetate, branched and straight-chain vinyl esters having a long chain, preferably having 7 to 15 carbon atoms such as vinyl pivalate, or vinyl ethylhexanoate, vinyl esters of saturated alpha-branched monocarboxylic acids having 5 or 9 to 11 carbon atoms, dialkyl maleates and dialkyl fumarates of C1- to C12-alcohols such as diisopropyl maleate and diisopropyl fumarate, vinyl chloride, vinyl alkyl ethers of alcohols having at least 4 carbon atoms, such as vinyl butyl ether, and C2- to C10-olefins such as ethene and decene. The imparting of hydrophobic properties can also be effected by polymerization of vinyl acetate in the presence of regulators such as alkyl mercaptans having a C2- to C18-alkyl radicals such as dodecyl mercaptan or tert-dodecyl mercaptan. A further possibility for imparting hydrophobic properties to polyvinyl acetate is by polymer-analogous reactions, for example acetylation of vinyl alcohol units in partially hydrolyzed polyvinyl acetate with C1- to C4-aldehydes such as butyraldehyde.
The proportion of hydrophobic units is preferably from 0.1 to 10% by weight, based on the total weight of the partially hydrolyzed polyvinyl acetate. The degree of hydrolysis is from 70 to 99.9 mol %, preferably from 84 to 92 mol %, and the Hxc3x6ppler viscosity (DIN 53015, Hxc3x6ppler method, 4% strength aqueous solution) is from 1 to 30 mPas, preferably from 2 to 15 mPas. Said protective colloids are obtainable by means of processes known to those skilled in the art.
The partially hydrolyzed polyvinyl acetates having from 84 to 92 mol % of vinyl alcohol units and from 0.1 to 10% by weight of units which are derived from vinyl esters of an alpha-branched carboxylic acid having 5 or 9 to 11 carbon atoms in the acid radical, isopropenyl acetate and ethene are particularly preferred as partially hydrolyzed polyvinyl esters which have been rendered hydrophobic; in particular the partially hydrolyzed polyvinyl acetates having vinyl alcohol units and units of vinyl esters of alpha-branched carboxylic acids having 5 or 9 to 11 carbon atoms in said amounts. Examples of such vinyl esters are those which are available as vinyl versatates from Shell, under the names VeoVaR5, VeoVaR9, VeoVaR10 and VeoVaR11. Combinations of the polyvinyl esters which have been mentioned as being particularly preferred and have been rendered hydrophobic with partially hydrolyzed polyvinyl acetates having a degree of hydrolysis of from 80 to 95 mol % and a Hxc3x6ppler viscosity of from 1 to 30 mPas, preferably from 2 to 15 mPas, which, in the form of a 2% strength aqueous solution, produce a surface tension of  greater than 40 mN/m, are also particularly preferred.
Further suitable protective colloids which can be used as a mixture with said polyvinyl alcohols are polyvinylpyrrolidones, carboxymethylcellulose, methyl-cellulose, hydroxyethylcellulose and hydroxypropyl-cellulose, starches, dextrins, cyclodextrins, poly(meth)acrylic acid, poly(meth)acrylamides, polyvinylsulfonic acids, melamine formaldehyde sulfonates, naphthalene formaldehyde sulfonates, and styrene/maleic acid and vinyl ether/maleic acid copolymers.
The protective colloids are added during the polymerization in general in a total amount of from 1 to 15% by weight, based on the total weight of the monomers. Where a protective colloid combination is used, the weight ratio of hydrophobic, partially hydrolyzed polyvinyl ester to nonhydrophobic, partially hydrolyzed polyvinyl alcohol, is from 10/1 to 1/10.
For controlling the molecular weight, regulating substances (regulators) are preferably used in the polymerization. Examples of such substances are n-dodecyl mercaptan, tert-dodecyl mercaptan, mercaptopropionic acid, methyl mercaptopropionate, isopropanol and acetaldehyde. They are usually used in amounts of from 0.01 to 5.0% by weight, preferably from 0.5 to 2.0% by weight, based in each case on the monomers to be polymerized.
For initiating the polymerization, all of the initiator is initially introduced, some of it is initially introduced and some metered, or all of the initiator is metered in. The total amount of the polyvinyl alcohol or the total amount of further protective colloid and the total amount of the comonomers can be initially introduced. Some can be initially introduced and some metered, or the total amounts can be metered. In a preferred embodiment, the total amount of protective colloid and from 5 to 25% by weight of the total amount of comonomer are initially introduced and the remaining amount of comonomer is metered in during the polymerization. In a further preferred embodiment, the total amount of protective colloid and the total amount of comonomer are initially introduced before initiation of the polymerization and polymerized in the presence of regulator. A procedure in which all of the protective colloid is initially introduced or some of the protective colloid is initially introduced and some of the amount of comonomer and some of the amount of regulator are initially introduced and the remainder in each case is metered in is also preferred. In a possible procedure here, comonomers and regulator are initially introduced and are metered in a constant ratio. The ratio of regulator to comonomer in the initially introduced mixture is greater than that during metering; for this purpose, preferably 15 to 50% by weight of the total amount of the regulator are initially introduced and from 5 to 25% by weight of the total amount of the comonomers are initially introduced.
When a protective colloid combination is used, one component of the protective colloid combination, preferably the hydrophobic, partially hydrolyzed polyvinyl ester, can be initially taken and the other component metered, or a part of the mixture initially taken and the remainder metered in as an aqueous solution.
After the end of the polymerization, postpolymerization can be effected using known methods for removing residual monomers, for example by postpolymerization initiated with a redox catalyst. Volatile residual monomers can also be removed by means of distillation, preferably under reduced pressure, and optionally while passing through or passing over inert entraining gases such as air, nitrogen or steam.
The aqueous dispersions obtainable with the process according to the invention have a solids content of from 30 to 75% by weight, preferably from 40 to 65% by weight. For the preparation of polymer powders redispersible in water, the aqueous dispersions are dried, for example by means of fluidized-bed drying, freeze-drying or spray-drying. Preferably, the dispersions are spray-dried. The spray-drying is effected in conventional spray drying units, it being possible to carry out the atomization by means of airless high-pressure nozzles, binary nozzles or multi-media nozzles or using a rotating disk. The outlet temperature is generally chosen in the range from 55xc2x0 C. to 100xc2x0 C., preferably from 70xc2x0 C. to 90xc2x0 C., depending on the unit, the Tg of the resin and the desired degree of drying.
The total amount of protective colloid before the drying process should preferably be at least 10% by weight, based on the amount of polymer. To ensure redispersibility, it is as a rule necessary to add further protective colloids as an atomization aid to the dispersion prior to drying. As a rule, the atomization aid is used in an amount of from 5 to 25% by weight, based on the polymeric components of the dispersion.
Suitable atomizing aids are partially hydrolyzed polyvinyl acetates; polyvinylpyrrolidones; polysaccharides in water-soluble form such as starches (amylose and amidopectin), celluloses and their carboxymethyl, methyl, hydroxyethyl and hydroxypropyl derivatives; proteins such as casein or caseinate, soy protein, gelatin; ligninsulfonates; synthetic polymers such as poly(meth)acrylic acid, copolymers of (meth)acrylates with comonomer units having carboxyl functional groups, poly(meth)acrylamide, polyvinyl-sulfonic acids and their water-soluble copolymers; melamine formaldehyde sulfonates, naphthalene formaldehyde sulfonates and styrene/maleic acid and vinyl ether/maleic acid copolymers. Preferred atomization aids are partially hydrolyzed polyvinyl acetate having a degree of hydrolysis of from 80 to 95 mol %, a Hxc3x6ppler viscosity of from 1 to 30 mPas, which may have been modified with isopropenyl acetate or vinyl ether units.
During the atomization, a content of up to 1.5% by weight of antifoam, based on the base polymer, has in many cases proven advantageous. For increasing the shelf-life by improving the blocking stability, in particular in the case of powders having a low glass transition temperature, an antiblocking agent (anticaking agent) can be added to the powder obtained, preferably in an amount of up to 30% by weight based on the total weight of polymeric components. Examples of antiblocking agents are calcium and magnesium carbonate, talc, gypsum, silica and silicates having particle sizes preferably in the range from 10 nm to 10 xcexcm.
For improving the performance characteristics, further additives may be added during the atomization. Further components of dispersion powder compositions, which are present in preferred embodiments are, for example, pigments, fillers, foam stabilizers and water repellents.
The polyvinyl alcohol-stabilized 1,3-diene/(meth)acrylic acid copolymers can be used in the form of their aqueous polymer dispersions or polymer powders redispersible in water, in the applications typical for them, for example, in chemical products for the building industry in combination with hydraulically setting binders such as cements (Portland cement, high-alumina cement, trass cement, slag cement, magnesia cement and phosphate cement), gypsum or waterglass, for the preparation of construction adhesives, renders, filling compounds, floor filling compounds, sealing slurries, joint mortars and paints, and furthermore, as sole binders for coating materials and adhesives or as coating materials or binders for textiles and paper.
An example of the use as an adhesive is the adhesive bonding of porous substrates such as the adhesive bonding of wood to give a wood-wood bond, the adhesive bonding of wood to absorptive substrates such as floor topping, in particular parquet bonding. Further applications are the water-resistant adhesive bonding of paper and board, for example, as packaging adhesive and bookbinding adhesive. As adhesives, the copolymers are also suitable for the adhesive bonding of fiber materials comprising natural or synthetic fibers, for example, for the production of wood fiberboards, for binding nonwovens comprising natural or synthetic fibers, with the production of moldings from fiber materials and for the production of precursors of such moldings, the so-called semifinished products (waddings). Further application examples are the binding of cotton, for example, of upholstery, insulation and filter waddings, and the production of laminates such as insulating materials.
Preference is given to the use as gypsum mortar for filling compounds, joint fillers, flowable CaSO4 floor toppings, joint compounds or adhesive mortars or the use for the production of plasterboards or plaster shapes. Further applications are, for example, renders or stucco work, including outdoors. The customary applications for the corresponding and modified CaCO3 materials are as joint fillers, gypsum-free filling compounds and renders. In general, the copolymer is used in an amount of from 0.2 to 15% by weight, based on the dry weight of the formulation.
The use in self-leveling floor filling compounds (leveling compounds) and floor toppings is also preferred. Preferably, from 0.5 to 10% by weight of dispersion powder, based on the dry weight of the formulation, are added. The formulations also contain from 5 to 80% by weight of inorganic, hydraulically setting binders, such as cement, gypsum or mixtures thereof. The formulation also contains from 5 to 80% by weight of inorganic fillers such as sand, quartz powder, chalk, limestone powder, filter ash or mixtures thereof. In order to improve the leveling properties, additives which promote leveling such as casein or cement liquefiers can, if required also be added to the dry mixture. The data in % by weight are always based on 100% by weight of dry mass in the formulation for floor filling compounds. The ready-to-use leveling compound is finally obtained by mixing water with the above-mentioned dry mixture.
The ready-to-use floor filling compound mixed with water can be used for the production of floor toppings and self-leveling coatings for leveling, evening out and smoothing surfaces.
A further preferred use of the dispersions and powders is that in cement-containing construction adhesive formulations. Typical formulations contain from 5 to 80% by weight of cement, from 5 to 80% by weight of fillers such as quartz sand, calcium carbonate or talc, from 0.1 to 2% by weight of thickeners such as cellulose ethers, sheet silicates or polyacrylates, from 0.5 to 60% by weight of the PVA1-stabilized (meth)acrylate/1,3-diene copolymers in the form of the polymer dispersion or the polymer powder and optionally, further additives for improving stability, processibility, open time and water resistance. The data in % by weight are always based on 100% by weight of dry mass of the formulation. Said cement-containing construction adhesive formulations are used in particular as tile adhesives for laying tiles of all kinds (earthenware, stoneware, porcelain, ceramic, natural tiles) indoors and outdoors and are mixed with the corresponding amount of water before their use.
An advantage of the (meth)acrylate/1,3-diene copolymers prepared according to the invention is their hydrolysis stability which improves with increasing 1,3-diene content compared with pure acrylate copolymers. Consequently, the mechanical copolymer properties such as tensile strength and elongation at break, remain unchanged even on application to alkaline surfaces. Furthermore, no toxicological controversial alcohols such as, for example, butanol or 2-ethylhexanol, or only small amounts thereof, are released on alkaline surfaces with such hydrolysis-stable systems. Compared with styrene/acrylate copolymers, the copolymers prepared according to the invention have, owing to their advantageous viscoelastic properties, in particular for adhesive applications, improved performance characteristics, in particular, high surface tack, high adhesion (peel strength) and high cohesion (shear stability). The outstanding cement stability, in particular of the copolymers stabilized with hydrophobically modified polyvinyl alcohols, is also noteworthy. The (meth)acrylate/1,3-diene copolymers prepared according to the invention also have the advantageous rheological properties (machine running properties) of vinyl ester or acrylate dispersions stabilized with polyvinyl alcohol.
The following examples serve for further explanation of the invention: